Pressure equalizing device for split brushes



March 28, 1967 v. E. MOWRY PRESSURE EQUALIZING DEVICE FOR SPLIT BRUSHES Filed Dec. 7, 1964 lA/l/E/VTOR. -V04/VEV f. MOWQY ATTORNEYS.

Fig.3

UnitedStates Patent This invention relates to split brushes for dynamoelectric machines, and more particularly to means for pressing the brushes against a commutator or current collector ring.

It is common practice on direct current traction motors of diesel-electric locomotives to use radial type brush holders, due to the fact that the motors must be capable of operating in both directions of rotation. It also has become standard practice to use with such brush holders carbon brushes that are split into two equal half-sections that are disposed side by side in a plane containing the axis of the motor. Until the advent of high horsepower traction motors a year or two ago, the outer ends of the brushes were provided with a convex curvature against which the spring-biased pressure fingers pressed. On the more recent high horsepower traction motors, there is a decided tendency for one brush half to wear at a considerably higher rate than the other brush half at the two extremes of loading; that is, heavy current, low voltage, low speed at one extreme, and light current, high voltage and high speed at the other extreme. As a result, since the pressure finger holding the brush halves on the commutator has applied pressure jointly to both halves of the brush at the apex of their convex ends, the brush half wearing at the slower rate has taken all of the pressure of the finger and prevented it from pressing against the other brush half that has the high rate of wear. With loss of pressure the brush half having thehigh rate of wear will lose contact with the commutator, resulting in excessive sparking. Thesparking will burn away that brush half, thereby causing a still greater rate of wear so that the objectionable condition becomes cumulative. Not only will the severe sparking damage the brushes, but it also will cause heavy damage to the commutator. If this situation continues for any length of time, the motor will become inoperative. In order to overcome the disadvantages just explained, a number of brush configurations have been proposed, but they all have disadvantages of their own.

It is among the objects of this invention to provide a device for insertion between a pressure arm and a pair of carbon brush half-sections, which will cause substantially equal pressure to be exerted against both brush sections even though one wears faster than the other, which has a rolling connection with the brush sections, which forces the brush sections apart and into frictional engagement with the surrounding brush holder, and which is simple and easy to make.

in accordance with this invention, a roller is adapted to be pressed by a pressure finger against the inwardly inclined outer end surfaces of a pair of carbon brush halfsections that are disposed side by side. At the opposite ends of the roller are means for rotatably supporting it, which are formed for connection to the four flexible shunt 'wires extending outwardly away from the outer endof the brush. Preferably, the supporting means for the roller include a pair of cross bars, each of which is pro- 331L768 Patented Mar. 28, 1967 ice vided near its ends with notches facing the other bar and adapted to loosely receive two of the shunt wires.

The preferred embodiment of the invention is illustrated in the accompanying drawings, in which FIG. 1 is an end view of a brush holder containing a split brush pressed against a current collector through my pressure equalizer;

FIG. 2 is a fragmentary plan view thereof; taken on the line IIII of FIG. 1;

FIG. 3 is a vertical section taken on the line III-III of FIG. 1;

FIG. 4 is an enlarged fragmentary view similar to FIG. 3, but showing the brush halves Worn unequally; and

FIG. 5 is a plan view, partly in section, of a modified pressure equalizer.

Referring to FIGS. 1, 2 and 3 of the drawings, a brush holder 1 of suitable well-known construction is mounted rigidly beside a rotating cylindrical current collector 2, such as the commutator or slip ring of a rotating electrical machine (not shown). Forconvenience of description only, the rotating collector will be referred to herein as a commutator. The machine is reversible so that the commutator can be rotated in either direction. The brush holder is provided at one end with a rectangular passage 3 that is disposed radially of the commutator and a short distance away from it. Pivoted to the opposite end of the brush holder is one end of a brush pressure finger d, the opposite end of which extends across the outer end of a carbon brush 5 that is slidably mounted in the brush holder passage. The central portion of the finger is connected to the brush holder beneath it by means of a coil spring 6 to cause the finger to press the brush against the commutator at all times.

As is common practice, the brush is formed from a pair of thin carbon half-sections A and B that are disposed side by side in the holder. The central portion of the outer end of each half-section has a surface s inclined inwardly across the brush section from near its outer face toward its inner face and end so that the brush as a whole appears to have a V-shape notch in its outer end, as shown in FIG. 3. At the opposite ends of the inclined surface of each brush half-section there .is a step 9, from which a flexible shunt wire ltl extends outwardly away from the brush. The outer ends of the four wires are connected in the usual manner by a common terminal 11.

It is a feature of this invention that even though one brush section may wear faster than the other, the pres sure of finger 4 against both half-sections will remain substantially uniform. At the same time, the brush halves will be urged apart toward the opposite sides of the brush holder passage, regardless of the direction of rotation of the commutator. As a result, vibration, chatter, chipping and breakage of the brush are greatly reduced or eliminated and the brush seat is not changed with reversal of the commutator. Accordingly, a pressure equalizing device is inserted in the V-notch between the pressure finger and the outer end of the brush. This device includes a roller 13 that is about as long as the inclined end surfaces 8 of brush sections A and B and that is large enough to prevent the finger from engaging the end of the brush while the roller is engaging its inclined surfaces. Pressure of the finger against the roller presses the blush against the commutator, while the pressure of the roller against the adjoining inclined surfaces of the brush halves tends to force those sections away from each other and against the adjoining sides of the brush holder passage 3.

The roller is rotatably supported in place by means connecting it with shunt wires 10. Thus, the opposite ends of the roller may be provided with necks 14 that extend into central passages 15 through a pair of short cross bars 16. As shown in FIG. 2, the necks are rotatably mounted in the bars and are provided with enlarged outer ends that fit in the enlarged outer ends of the passages. The necks and bars may be assembled by providing the necks with longitudinal slots 17 extending inwardly from their outer ends in order to separate each neck into three or more spaced segments that can be sprung toward each other far enough to permit the enlarged outer end of the neck to pass through the smaller part of the bar passage. To connect the cross bars to the shunt wires, each bar may be provided at opposite sides of the adjoining neck with notches 18 facing the other bar for loosely receiving two of the shunt wires at one side of the brush holder. The roller thus will be suspended between the two pairs of shunt wires and becomes a removable part of the brush assembly.

In case one brush half-section wears at a faster rate than the other, as shown in FIG. 4, the roller 13 is free to roll down the inclined end surface a of the half-section A with the lesser rate of wear, whereby to remain in engagement with the other section B. The cross bars will permit this movement of the roller because they can shift sideways and tilt to some extent and the shunt wires can bend easily. Actually, there is very little likelihood of one brush section becoming more than one-eighth inch shorter than the other half due to wear. Of course, if it is section A that wears faster, then the roller will roll down the inclined end surface of section B. Since the roller can freely accommodate itself to the two unequal brush sections by rolling against their outer ends, the pressure that it transmits to them from the pressure finger will remain substantially uniform. Likewise, the roller will continue to urge the brush sections toward the opposite sides of the brush holder passage.

The notched cross bars at the ends of the roller allow it to roll and adjust for the difference in wear between the two sections of the brush. The bars remain attached to the shunt wires during normal handling of the brush assembly, such as during inspection, shipping and installation. On the other hand, they can be removed easily from the shunts and used again with a new brush.

The roller may be made of any material of suitable strength and heat resistant qualities. A satisfactory material is a plastic such as nylon or Teflon or Micarta. Or, a resilient rubber-like material may be used if desired. If any of these dielectric materials are used, it is not necessary to insulate the pressure finger from the roller. Due to a roller being used, the restraint that may be encountered with sliding surfaces can be avoided.

In the embodiment of the invention shown in FIG. 5, the roller 21 is hollow and turns on a pair of aligned shafts 22 extending into it from its opposite ends. The two shafts are connected together inside of the roller, preferably by inter-engaging snap hooks. Thus, the inner end of each shaft may be provided with a longitudinally extending elongated hook 23 that is offset from the axis of the roller. When the two shafts are properly oriented and then pushed into the opposite ends of the roller, the two hooks will ride over each other and snap into permanent connection with each other. Secured to the outer end of each shaft is a separate or integral cross bar 24 provided with a pair of notches 25 for loosely receiving a pair of the brush shunt wires in order to connect the roller to the shunts. When one brush half-section wears more rapidly than the other half, the roller will rotate on its supporting shafts and continue to press against both brush halves with substantially the same have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. A pressure equalizing device for insertionbetween a pressure finger and the inwardly inclined outer end surfaces of a pair of carbon brush half-sections side by side and each having a pair of flexible shunt wires extending outwardly away from its outer end, said device comprising a roller adapted to be pressed against said inclined surfaces by said finger, and means at the opposite ends of the roller rotatably supporting it, said means being formed for connection to said shunt wires.

2. A pressure equalizing device for insertion between a pressure finger and the inwardly inclined outer end surfaces of a pair of carbon brush half-sections side by side and each having a pair of shunt wires extending outwardly away from its outer end, said device comprising a roller adapted to be pressed against said inclined surfaces by said finger, and means at the opposite ends of the roller rotatably supporting it, said means including a pair of cross bars, each bar being provided near its ends with notches facing the other bar and adapted to loosely receive two of said shunt wires.

3. A pressure equalizing device for insertion between a pressure finger and the inwardly inclined outer end surfaces of a pair of carbon brush half-sections. side by side and each having a pairof shunt wires extending outwardly away from its outer end, said device comprising a roller adapted to be pressed against said inclined surf-aces by said finger, the roller being provided with necks at its opposite ends, and means mounted on said necks and rotatably supporting them, said means being formed for loose connection to said shunt wires.

A pressure equalizing device according to claim 3, in which said means are cross bars provided with central passages rotatably receiving said necks, the outer ends of the necks being enlarged, the outer ends of said passages being enlarged to receive the enlarged ends of the necks, and the necks being provided with longitudinal slots extending inwardly from their outer ends to separate each neck into spaced segments that can be sprung toward each other'to allow insertion of the neck in one of said passages.

5. A pressure equalizing device for insertion between a pressure finger and the inwardly inclined outer end surfaces of a pair of carbon brush half-sections side by side and each having a pair of shunt wires extending outwardly away from its outer end, said device comprising a hollow roller adapted to be pressed against said inclined surfaces by said finger, a pair of aligned shafts rotatably disposed inside the roller and projecting from its ends, the inner ends of the shafts being connected together, and a cross bar secured to the outer end of each shaft and for-med for connection to two of said shunt wires.

6. A pressure equalizing device according to claim 5, in which the inner ends of said rollers are provided with interengaging spring hooks connecting them together.

'7. A pressure equalizing device according to claim 5, in which eachcross bar is provided near its ends with notches facing the other bar and adapted to loosely receive two of said shunt wires.

8. A pressure equalizing device for insertion between a pressure finger and the inwardly inclined outer end surfaces of a pair of carbon brush half-sections side by side and each having a pair of shunt wires extending outwardly away from its outer end, said device comprising a hollow roller adapted to be pressed against said inclined surfaces by said finger, a pair of aligned shafts rotatably disposed inside the roller and projecting from its ends, the inner ends of said rollers being provided with longitudinally extending interengaging spring hooks connecting them together, and a cross bar rigidly mounted on the outer end of each shaft, each bar being provided near its ends with notches facing the other bar and adapted to loosely receive two of said shunt wires.

9. A pressure equalizing device for insertion between a pressure finger and the inwardly inclined outer end surfaces of a pair of carbon brush half-sections side by side and each having a pair of shunt wires extending outwardly away from its outer end, said device comprising a roller adapted to be pressed against said inclined surfaces by said finger, the roller having axial openings in its ends, a pair of aligned shafts rotatably disposed in said openings and projecting therefrom, means inside the roller ends of the shafts and formed for loose connection to said shunt wires.

References Cited by the Examiner UNITED STATES PATENTS 2,579,565 12/1951 Giambonini 310246 2,796,544 6/1957 Silverman 310-246 3,158,772 11/1964 Krellner 310246 FOREIGN PATENTS 1,020,066 2/1953 France.

18,777 7/ 1913 Great Britain.

MILTON O. HIRSHFIELD, Primary Examiner.

holding the shafts therein and means secured to the outer 15 11F. DUGGAN, Assistant Examiner. 

9. A PRESSURE EQUALIZING DEVICE FOR INSERTION BETWEEN A PRESSURE FINGER AND THE INWARDLY INCLINED OUTER END SURFACES OF A PAIR OF CARBON BRUSH HALF-SECTIONS SIDE BY SIDE AND EACH HAVING A PAIR OF SHUNT WIRES EXTENDING OUTWARDLY AWAY FROM ITS OUTER END, SAID DEVICE COMPRISING A ROLLER ADAPTED TO BE PRESSED AGAINST SAID INCLINED SURFACES BY SAID FINGER, THE ROLLER HAVING AXIAL OPENINGS IN ITS ENDS, A PAIR OF ALIGNED SHAFTS ROTATABLY DISPOSED IN SAID OPENINGS AND PROJECTING THEREFROM, MEANS INSIDE THE ROLLER HOLDING THE SHAFTS THEREIN AND MEANS SECURED TO THE OUTER ENDS OF THE SHAFTS AND FORMED FOR LOOSE CONNECTION TO SAID SHUNT WIRES. 